1. Field of the Invention
The present invention is concerned with mounting arrangements. The invention is concerned with, for example, mounting arrangements for use in heating assemblies, such as anti-icing assemblies, of gas turbine engines.
During use of a gas turbine engine, for example a gas turbine engine mounted on the wing of an aircraft, ice may form on various parts of the engine. For example, ice may form on surfaces of the engine intake, such as towards the leading surfaces of the nacelle. The ice may form in a variety of conditions, for example during flight through clouds containing supercooled water droplets and/or on the ground in freezing fog.
Ice attached to the surface of the gas turbine engine may effectively change the geometry of the surface to which it is attached, such that oncoming flow is presented with a surface that is not to design specification. For example, ice formation may reduce the size of the engine air intake below design specification. This may ultimately result in lower engine efficiency and/or performance. A further problem may be caused by ice that has formed on the engine surface breaking free in an uncontrolled manner. This could lead to ice being ingested into the engine, which could lead to damage and/or further loss of efficiency.
It is therefore desirable to provide an anti-icing system that controls, for example by substantially eliminating, ice formation on the engine surfaces. Arrangements of anti-icing systems comprise tubes that are supplied with hot air. The tubes contain holes through which the hot air can escape. Through these holes, the hot air can be provided to surfaces that are susceptible to ice formation. An example of such an anti-icing arrangement is an annular tube provided inside the leading edge of the nacelle (or engine intake). Such an annular tube may be provided with heated air, which may be from the compressor, which may then be directed as required to the leading edge surfaces of the nacelle through the holes formed therein. Such an arrangement acts to heat the leading edge surfaces of the nacelle, thereby preventing/reducing ice formation.
It is necessary to fix the annular tube in the desired position, which in the case of the example above may be inside the leading edge of the nacelle. However, during operation of the anti-icing system, the annular tube may change shape. In particular, the annular tube may radially expand (with respect to the engine axis). This may be due to thermal expansion resulting from being supplied with hot air and/or expansion due to pressure of the air supplied to the ring, which may, for example, be from the exit of the compressor. As such, the mounting arrangement used to attach the annular tube to the engine must be able to accommodate such radial expansion.
2. Description of the Related Art
An example of a known anti-icing arrangement 25 is shown in FIGS. 1 and 2. The anti-icing arrangement 25 is located inside a nacelle 11, and comprises a heating pipe 30 attached to a bulkhead 40 of the engine using mounting brackets 50. Each mounting bracket 50 has an arm 52 that is rotatably mounted at one end to a fixing 54 on the bulkhead 40. The arm 52 is rotatably mounted at its other end to a bangle 56. The bangle 56 is fixed, for example welded, to the heating pipe 30. This in itself can lead to residual stresses and/or distortion in the heating pipe 30 and/or the mounting bracket 50. Any distortion may lead to misalignment and/or further stresses during assembly of the full anti-icing arrangement.
Typically, the heating pipe 30 is annular. As mentioned above, in use, the annular heating pipe 30 may experience radial expansion relative to the engine axis, as indicated by the arrow 60 in FIG. 2. In order to accommodate this radial expansion 60, the rotatable joint 53 between the arm 52 and the fixing 54 pivots, as does the rotatable joint 55 between the arm 52 and the bangle 56. In FIG. 2, arrow 62 represents the rotation of the arm 52 about the joint 53, and arrow 64 represents rotation of the bangle 56 about the joint 55 in response to radial expansion 60 of the annular heating pipe 30.
The arrangement shown in FIGS. 1 and 2 therefore requires joints 53, 55 that allow the arm 52 to pivot relative to both the fixing 54 and the bangle 56. These joints 53, 55 therefore require bearings, bushes, and/or sleeves to allow for the pivoting. These bearings/bushes/sleeves may fail, for example seize. This may be caused by repeated radial expansion/contraction of the heating pipe 30. The problem may be exacerbated by temperature fluctuations that may be caused by the heat provided to the anti-icing system, and/or by the presence of any contaminants. If the bearings/bushes/sleeves fail/seize, any radial expansion of the heating pipe 30 cannot be accommodated by the mounting bracket 50 through rotation of the joints 53, 55. This may induce stress in the heating pipe 30 and/or the mounting bracket 50, which may lead to failure of the heating pipe 30 and/or the mounting bracket 50. Thus, the FIGS. 1 and 2 arrangement may be considered to be heavy and relatively complicated, and/or susceptible to failure.